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From: Jason Gunthorpe <jgg@ziepe.ca>
To: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Cc: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
	Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
	davem@davemloft.net, gregkh@linuxfoundation.org,
	netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
	nhorman@redhat.com, sassmann@redhat.com,
	Fred Oh <fred.oh@linux.intel.com>
Subject: Re: [net-next v4 10/12] ASoC: SOF: Introduce descriptors for SOF client
Date: Fri, 22 May 2020 11:55:42 -0300	[thread overview]
Message-ID: <20200522145542.GI17583@ziepe.ca> (raw)
In-Reply-To: <7abfbda8-2b4b-5301-6a86-1696d4898525@linux.intel.com>

On Fri, May 22, 2020 at 09:29:57AM -0500, Pierre-Louis Bossart wrote:
> 
> > > > > +	ret = virtbus_register_device(vdev);
> > > > > +	if (ret < 0)
> > > > > +		return ret;
> > > > > +
> > > > > +	/* make sure the probe is complete before updating client list
> > > > > */
> > > > > +	timeout = msecs_to_jiffies(SOF_CLIENT_PROBE_TIMEOUT_MS);
> > > > > +	time = wait_for_completion_timeout(&cdev->probe_complete,
> > > > > timeout);
> > > > 
> > > > This seems bonkers - the whole point of something like virtual bus is
> > > > to avoid madness like this.
> > > 
> > > Thanks for your review, Jason. The idea of the times wait here is to
> > > make the registration of the virtbus devices synchronous so that the
> > > SOF core device has knowledge of all the clients that have been able to
> > > probe successfully. This part is domain-specific and it works very well
> > > in the audio driver case.
> > 
> > This need to be hot plug safe. What if the module for this driver is
> > not available until later in boot? What if the user unplugs the
> > driver? What if the kernel runs probing single threaded?
> > 
> > It is really unlikely you can both have the requirement that things be
> > synchronous and also be doing all the other lifetime details properly..
> 
> Can you suggest an alternate solution then?

I don't even know what problem you are trying to solve.

> The complete/wait_for_completion is a simple mechanism to tell that the
> action requested by the parent is done. Absent that, we can end-up in a
> situation where the probe may fail, or the requested module does not exist,
> and the parent knows nothing about the failure - so the system is in a
> zombie state and users are frustrated. It's not great either, is it?

Maybe not great, but at least it is consistent with all the lifetime
models and the operation of the driver core.

> This is not an hypothetical case, we've had this recurring problem when a
> PCI device creates an audio card represented as a platform device. When the
> card registration fails, typically due to configuration issues, the PCI
> probe still completes. That's really confusing and the source of lots of
> support questions. If we use these virtual bus extensions to stpo abusing
> platform devices, it'd be really nice to make those unreported probe
> failures go away.

I think you need to address this in some other way that is hot plug
safe.

Surely you can make this failure visible to users in some other way?

Jason

  reply	other threads:[~2020-05-22 14:55 UTC|newest]

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-20  7:02 [net-next v4 00/12][pull request] 100GbE Intel Wired LAN Driver Updates 2020-05-19 Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 01/12] Implementation of Virtual Bus Jeff Kirsher
2020-05-21 14:57   ` Parav Pandit
2020-05-21 17:43     ` gregkh
2020-05-21 20:10       ` Jason Gunthorpe
2020-05-20  7:02 ` [net-next v4 02/12] ice: Create and register virtual bus for RDMA Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 03/12] ice: Complete RDMA peer registration Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 04/12] ice: Support resource allocation requests Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 05/12] ice: Enable event notifications Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 06/12] ice: Allow reset operations Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 07/12] ice: Pass through communications to VF Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 08/12] i40e: Move client header location Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 09/12] i40e: Register a virtbus device to provide RDMA Jeff Kirsher
2020-05-20  7:02 ` [net-next v4 10/12] ASoC: SOF: Introduce descriptors for SOF client Jeff Kirsher
2020-05-20  7:20   ` Greg KH
2020-05-20 12:54   ` Jason Gunthorpe
2020-05-20 12:57     ` Jason Gunthorpe
2020-05-21 21:11     ` Ranjani Sridharan
2020-05-21 23:34       ` Jason Gunthorpe
2020-05-22 14:29         ` Pierre-Louis Bossart
2020-05-22 14:55           ` Jason Gunthorpe [this message]
2020-05-22 15:33             ` Pierre-Louis Bossart
2020-05-22 17:10               ` Jason Gunthorpe
2020-05-22 18:35                 ` Pierre-Louis Bossart
2020-05-22 18:40                   ` Jason Gunthorpe
2020-05-22 18:48                     ` Pierre-Louis Bossart
2020-05-22 19:44                       ` Jason Gunthorpe
2020-05-22 21:05                         ` Pierre-Louis Bossart
2020-06-29 20:59               ` Mark Brown
2020-05-23  6:23           ` Greg KH
2020-05-23 19:41             ` Pierre-Louis Bossart
2020-05-24  6:35               ` Greg KH
2020-05-26 13:15                 ` Pierre-Louis Bossart
2020-05-26 13:37                   ` Takashi Iwai
2020-05-27  7:17                     ` Greg KH
2020-05-27 14:05                       ` Pierre-Louis Bossart
2020-06-29 20:33                       ` Mark Brown
2020-06-29 22:59                         ` Jason Gunthorpe
2020-06-29 23:13                           ` Kirsher, Jeffrey T
2020-06-30 10:31                           ` Mark Brown
2020-06-30 11:32                             ` Jason Gunthorpe
2020-06-30 14:16                               ` Mark Brown
2020-06-30 17:24                               ` Ranjani Sridharan
2020-06-30 17:27                                 ` Jason Gunthorpe
2020-07-01  9:50                                   ` Mark Brown
2020-07-01 23:32                                     ` Jason Gunthorpe
2020-07-02 11:15                                       ` Mark Brown
2020-07-02 12:11                                         ` Jason Gunthorpe
2020-07-02 12:20                                           ` Mark Brown
2020-07-01  6:59                                 ` Greg KH
2020-07-02 13:43                                   ` Ranjani Sridharan
2020-07-06 23:02                                     ` Dan Williams
2020-07-07 14:16                                       ` Greg KH
2020-05-25 16:55               ` Jason Gunthorpe
2020-06-29 20:21             ` Mark Brown
2020-06-29 17:36   ` Mark Brown
2020-05-20  7:02 ` [net-next v4 11/12] ASoC: SOF: Create client driver for IPC test Jeff Kirsher
2020-05-20  7:22   ` Greg KH
2020-05-20 12:56   ` Jason Gunthorpe
2020-05-27 20:18     ` Ranjani Sridharan
2020-05-28  0:12       ` Jason Gunthorpe
2020-05-28  1:40         ` Ranjani Sridharan
2020-05-28 10:45           ` Greg KH
2020-06-29 20:37             ` Mark Brown
2020-05-20  7:02 ` [net-next v4 12/12] ASoC: SOF: ops: Add new op for client registration Jeff Kirsher
2020-05-20  7:23   ` Greg KH
2020-05-20  7:17 ` [net-next v4 00/12][pull request] 100GbE Intel Wired LAN Driver Updates 2020-05-19 Greg KH
2020-05-20  7:25   ` Kirsher, Jeffrey T
2020-05-20  9:08     ` Greg KH

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